1. Field of the Invention
The subject invention relates to flexible bismaleimides which are prepared through the reaction of maleic anhydride with an amino-terminated polyoxybutylene.
2. Description of the Related Art
Bismaleimide resins are heat curable reactive resins which are finding increasing applications in the aerospace, automotive, machine construction and electronic fields, for example, in the form of filled and unfilled molding compositions, as well as fiber reinforced prepregs. These thermosetting materials show good heat resistance and high modulus of elasticity, however they share a major disadvantage in their comparatively high degree of brittleness. This characteristic is thought to be caused by the high crosslinking density. When these materials are used as structural components in the aerospace industry, the fiber reinforced composite materials used are faced with severe requirements in terms of ductility and toughness, which cannot be satisfactorily fulfilled by presently available bismaleimide resins.
The use of rubber to toughen bismaleimide resins has not proven successful for a variety of reasons. A different concept resides in incorporation of flexible chain segments into the polymer network through the use of maleimide-group terminated polymers. However, up until now, such flexible bismaleimides have not possessed the range of properties necessary for their intended applications.